1. Field of the Invention
The present invention relates, in general, to nano-dispersed catalyst powders, and, more particularly, to nano-dispersed, complex composition fine powders and methods to produce such powders.
2. Background of the Invention
Powders are used in numerous applications. They are the building blocks of catalytic, electronic, telecommunication, electrical, magnetic, structural, optical, biomedical, chemical, thermal and consumer goods. On-going market demands for more efficient, reliable, smaller, faster, superior and more portable products have demanded miniaturization of numerous products. This, in turn, has demanded miniaturization of the building blocks, i.e. the powders. Sub-micron and nanoscale (or nanosize, ultra-fine) powders, with a size 10 to 100 times smaller than conventional micron size powders, enable quality improvement and differentiation of product characteristics at scales currently unachievable by commercially available micron-sized powders.
Nanopowders in particular, and sub-micron powders in general, are a novel family of materials whose distinguishing features include that their domain size is so small that size confinement effects become a significant determinant of the materials"" performance. Such confinement effects can, therefore, lead to a wide range of commercially important properties. Nanopowders, therefore, are an extraordinary opportunity for design, development and commercialization of a wide range of devices and products for various applications. Furthermore, since they represent a whole new family of material precursors where conventional coarse-grain physiochemical mechanisms are not applicable, these materials offer unique combination of properties that can enable novel and multifunctional components of unmatched performance. Bickmore, et al. in U.S. Pat. No. 5,984,997, which along with the references contained therein is incorporated herein by reference, teach some applications of sub-micron and nanoscale powders.
Conventional dispersed powders comprise powders of a first composition (e.g. metal) dispersed on the surface of a carrier which may be of a second composition (e.g. carbon). The dispersed powder structure enables greater and more effective availability of the first composition. It also provides a cost reduction because the second composition can be a low-cost carrier. Additionally, the dispersed powder structure improves the stability and enhances the performance synergistically.
Dispersed powders are desired in a number of applications such as catalysis. The junctions provide active sites for useful chemical reactions. Dispersed powders are often produced using chemical precipitation techniques. These techniques fail to provide a fine and uniform distribution of the dispersed particles on the surfaces of the carrier. Furthermore, the challenge becomes even more difficult when complex compositions need to be dispersed on a carrier powder. Chemical precipitation techniques also leave chemical residues on the surfaces that sometimes are not desirable. Given the difficulty in their production, few dispersed powders are known in the literature and these have found only limited applications.
Phillips in U.S. Pat. No. 5,989,648 (which, along with its references, is specifically incorporated herein by reference) teaches a plasma-based method for preparing metal supported catalysts from an aerosol comprising a mixture of at least one metal powder and at least one support powder. Phillips reports the unusual benefits as catalysts of the metal supported powders so prepared. However, Phillips does not offer motivation for or methods of utilizing fluid precursors to form dispersed powders. Phillips also does not teach nano-dispersed sub-micron powders, motivations for their use, or their benefits to various applications.
Briefly stated, the present invention involves nano-dispersed powders comprising powders that have been morphologically engineered. More specifically, the term nano-dispersed powders according to this invention refers to powders that have been arranged to provide a desired morphological distribution (dispersion) at nanoscale levels (e.g., sub-100 nm levels). As described in the definition section, nano-dispersed powders comprise carrier particles and attached particles dispersed on the surface of the carrier particles.
The carrier particles may be spherical, non-spherical, porous, tubular, planar, crystallites, amorphous, or any other useful form. The nanoparticles may similarly be one-dimensional, two-dimensional, or three-dimensional, spherical, non-spherical, porous, tubular, planar, crystallites, or amorphous forms, or any other useful form. The attached nano-dispersed particles may be free flowing, agglomerated, porous, coated, or hollow forms or any other useful form. The same carrier may have nanoparticles of more than one composition attached to its surface. In addition, various nano-dispersed particles of different compositions may be blended to achieve useful compositions.
The invention provides nano-dispersed powders with unusually engineered morphology. The unusual morphology provides a high density of multi-phasic points (i.e. points where two or more distinct phases interact with each other and/or species in the gas phase). These morphologically engineered nano-dispersed powders offer benefits to numerous applications. Some illustrative, but non-limiting applications include (a) catalytic transformation of less valuable chemicals and material feed stocks into more valuable chemicals and materials; (b) catalytic transformation of more hazardous chemicals and materials into less hazardous or non-hazardous forms of substances; (c) unusual phosphor, photonic, and optical materials for display, photonic, and optical applications; (d) unusual carriers, tracers, drug delivery vehicles, and markers for biomedical and genomic applications; (e) unusual building blocks for batteries, sensors, and electrochemical products; (f) fillers for polymers, ceramics, and metal matrix composites; and (g) dopants for electronic, magnetic, thermal, piezo, electrical, tooling, structural, inks, paints, and topical health products.
The concept of dispersed powders disclosed and their methods of manufacture may be applied to produce commercially useful submicron and micron dispersed powders as well.